End-contact type thermal head and manufacturing method therefor

Abstract: A slope (18) is provided from a heater area (13) to the side of the edge of a substrate (10) near the heater area (13). A resistance film layer (12) and a common electrode (15) are provided on the slope (18) which is formed as a convexly curved surface. In the slope (18), a reinforcement conductor along the common electrode (15) is embedded below the resistance film layer (12).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a thermal head and more particularly to a corner head type thermal head improved in printing efficiency and a manufacturing method therefor. 2. Description of the Related Art In using a thermal head, it is necessary to concentrate pressure on a ribbon, print paper, and a platen in a heater area for supporting print on rough paper and improving printing efficiency. For this purpose, hitherto, a near edge type thermal head with a heater area provided near the edge of the thermal head has been installed so as to be inclined against a platen for concentrating pressure against a ribbon and print paper on the heater area and its vicinity. Such a near edge type thermal head is disclosed, for example, in Japanese Utility Model Publication No.Hei 4-46929. An example of the head is shown in Figures 28 and 29. Figure 28 shows a sectional view of the near edge type thermal head, wherein a glaze layer is formed on a substrate 10 and a resistance film layer 12, electrodes 14 and 15, and a protective film are provided thereon. To use the thermal head, print paper 30 is placed under a platen 51 and from under the print paper, a ribbon 31 is pressed onto the print paper 30 by the thermal head 50, as shown in Figure 29. At this time, the thermal head 50 is supported by a carriage so that it is inclined against the platen 41. As shown in Figure 28, a slope 18 constituted by a part of the glaze layer 11 and a part of the substrate 10 is formed on the edge of the thermal head 50 for facilitating passage of the ribbon 31 when the thermal head 50 is inclined. However, the intersecting part 55 of the slope 18 and the top surface of the glaze layer 11, namely, the corner part 55 is not applied on a heater area 13. The near edge type thermal head has a heater part having a small curvature and the heater area formed so as not to lie across the corner part 55, thus the inclination angle of the thermal head against the platen 51 cannot be made large. The angle is from several degrees to less than 10 degrees at most. Therefore, concentration of pressure on the ribbon and print paper cannot be made so high with the result that printing efficiency is insufficient and a good print on rough paper cannot be provided. To solve the problem, a corner head type thermal head is used with the above-mentioned corner part formed in a glaze layer located near the edge of the thermal head and a heater area formed so as to lie across the corner part. Examples of such a corner head type thermal head are shown in Figures 30 and 31(a),(b). Figure 30 shows a sectional view of an example of the conventional corner head type thermal head, wherein a glaze layer 11 is formed on a substrate 10 and a resistance film layer 12 is formed on the glaze layer 11. The glaze layer 11 in the example is of partial glaze type and has the sectional form like a mountain. A heater area 13 with a predetermined part generating heat when the print operation is performed is formed on the top of the mountain. A slope 18 is provided from the heater area 13 to the side 17 of the substrate 10 edge near the heater area 13. A common electrode 15 is provided on the slope 18. A discrete electrode 14 for supplying a current to the predetermined part of the heater area 13 in conjunction with the common electrode 15 is formed in an area on the resistance film layer 12, the area facing the common electrode 15 with the heater area 13 between. In the example, current flows from the common electrode 15 via the resistance film layer 12 of the heater area 13 into the discrete electrode 14. As seen in Figure 30, the slope 18 end on the side of the glaze layer 11, namely, the corner part 55 is formed so as to be applied on the heater area 13. Therefore, the heater area 13 is formed so as to lie across the corner part 55. A protective film 16 is formed on the top layer. Figures 31(a),(b) show another example of the conventional corner head type thermal head. Parts identical with or similar to those previously described with reference to Figure 30 are denoted by the same reference numerals in Figures 31(a),(b) and will not be discussed again. Figure 31 (a) shows a sectional view of the thermal head in the example. A discrete electrode 14 and a common electrode 15 are provided on the same side with respect to a heater area 13 and a turned common electrode 45 is provided facing the discrete electrode 14 and the common electrode 15 with the heater area 13 between. Their arrangement is shown as a partial plan view in Figure 31 (b), wherein supply voltage is supplied to the common electrodes 15 and current flows into the discrete electrodes 14 via the heater area 13 and the turned common electrodes 45. Next, Figure 32 shows a use example of the conventional corner head type thermal head. In Figure 32, the corner head type thermal head 50 is installed so as to be inclined against a platen 51 for concentrating pressure against a ribbon 31 and print paper 30 on the heater area 13. In the example, the inclination angle of the corner head type thermal head can be made larger than that of the near end type thermal head; normally, it can be set to about 10 degrees to 35 degrees. The curvature of the heater part of the corner head type thermal head can also be made larger than that of the near end type thermal head. Thus, the concentration of pressure is raised, improving the printing efficiency. However, since the slope 18 is flat, the intersecting part 20 of the side of the thermal head and the slope 18 has a corner. The curvature of the heater part becomes large, the head sinks into the ribbon 31 and print paper 30 deeply, and the inclination angle increases, so that the intersecting part 20 approaches the ribbon 31, etc., compared with the near edge type thermal head. Thus, the ribbon 31 is in sliding contact with the top of the intersecting part 20 and is worn or cut. Dirty print occurs on print paper 30 because of powder from the ribbon 31. Further, if thermosensible paper is used as print paper 30, it is also in sliding contact with the top of the intersecting part 20, causing pressure rubbing of the paper, so that it causes a mark. In the example of the conventional corner head type thermal head shown in Figure 30, the width of the slope 18, L, is about 200 µm. Therefore, the width of the common electrode 15 formed in the part is limited to 200 µm or less. If the common electrode 15 is made thicker, a disadvantage such as catching of the ribbon occurs and the thickness is also limited. Thus, if the heater area is lengthened or the number of heaters is increased in the conventional corner head type thermal head, the resistance value of the common electrode 15 becomes large and the voltage drop at the parts far from the part to which supply voltage is supplied becomes large, degrading the printing quality. On the other hand, in the example of the conventional corner head type thermal head shown in Figure 31, a power supply is connected to each of the common electrodes 13 individually, thus the voltage drop can be reduced and the problem in the example in Figure 32 can be dealt with. However, in the example shown in Figure 33, the substantial area of the heater area 13 corresponding to one picture element becomes twice that in the example shown in Figure 32; the corner head type thermal head in the example shown in Figure 33 is not applicable to an application where a fine pattern is required. EP-A-0 497 551 shows a thermal printing head having a substrate, a glaze layer, a resistance film layer, electrodes facing each other, and a heater area provided between the electrodes. A slope formed as a convexly curved surface is provided from a predetermined position on a top face of said glaze layer to a substrate side. However, the intersection of the slope and the substrate side is not curved. JP-A-4-169 274 discloses a thermal printing head having a glaze layer formed on the top surface and a convexly curved slope of a substrate. A resistance film layer and electrodes are formed thereon to provide a heating area which is disposed on a corner part formed by intersection of the slope and the top face of said glaze layer. Another thermal printing head shown in JP-A-4-169 247 includes an additional layer which may be regarded as a reinforcement conductor. This additional layer is provided on the convexly curved slope of the substrate below the resistance film layer. Further, JP-A-4-169 274 discloses a third thermal printing head the substrate of which has a linear slope. In this area the resistance film layer is sandwiched between an additional layer (may be a reinforcement conductor) and a common electrode. A thermal head known from JP-A-4-039 064 comprises a reinforcement conductive layer with a smooth surface. This conductive layer is disposed below a resistance film layer of a heating element and associated with a common electrode. SUMMARY OF THE INVENTION It is an object of the present invention to provide a corner head type thermal head having a reduced resistance value of common electrodes. Another object of the present invention is to provide a method of manufacturing such a thermal head. This object is achieved by the subject matter of claim 1 and claim 4, respectively. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Figure 1 is a sectional view of a corner head type thermal head according to a first embodiment of the invention; Figure 2 is a sectional view of a corner head type thermal head according to a second embodiment of the invention; Figure 3 is a sectional view of a corner head type thermal head according to a third embodiment of the invention; Figure 4 is a sectional view of a corner head type thermal head according to a fourth embodiment of the invention; Figure 5 is a sectional view of a corner head type thermal head according to a fifth embodiment of the invention; Figure 6 is a sectional view of a corner head type thermal head according to an sixth embodiment of the invention; Figure 7 is a sectional view of a corner head type thermal head according to a seventh embodiment of the invention; Figure 8 is a sectional view of a corner head type thermal head according to a eighth embodiment of the invention; Figure 9 is a process drawing showing a step in a manufacturing method of the corner head type thermal head; Figure 10 is a process drawing showing a step in the manufacturing method of the corner head type thermal head; Figure 11 is a process drawing showing a step in the manufacturing method of the corner head type thermal head; Figure 12 is a process drawing showing a step in the manufacturing method of the corner head type thermal head; Figure 13 is a process drawing showing a step in the manufacturing method of the corner head type thermal head; Figure 14 is an illustration of a printing mechanism of a printer using the corner head type thermal head according to the invention; Figure 15(a) is an illustration of a method of manufacturing a corner head type thermal head of full glaze type according to the invention; Figure 15(b) is a sectional view of a corner head type thermal head of full glaze type according to the invention; Figure 16(a) is an illustration of a method of manufacturing the corner head type thermal head; Figure 16(b) is a sectional view of a corner head type thermal head manufactured by the method of Figure 16(a); Figure 17 is a sectional view of another corner head type thermal head Figure 18 is a process drawing showing a step in a manufacturing method of the corner head type thermal head in Figure 1; Figure 19 is a process drawing showing a step in the manufacturing method of the corner head type thermal head in Figure 1; Figure 20 is a process drawing showing a step in the manufacturing method of the corner head type thermal head in Figure 1; Figure 21 is a process drawing showing a step in the manufacturing method of the corner head type thermal head in Figure 1; Figure 22 is a process drawing showing a step in the manufacturing method of the corner head type thermal head in Figure 1; Figure 23 is a process drawing showing a step in the manufacturing method of the corner head type thermal head in Figure 1; Figure 24 is a process drawing showing a step in a manufacturing method of the corner head type thermal head in Figure 5; Figure 25 is a process drawing showing a step in the manufacturing method of the corner head type thermal head in Figure 5; Figure 26 is a process drawing showing a step in the manufacturing method of the corner head type thermal head in Figure 5; Figure 27 is a process drawing showing a step in the manufacturing method of the corner head type thermal head in Figure 5; Figure 28 is a sectional view of an example of a conventional near edge type thermal head; Figure 29 is an illustration of a printing mechanism of a printer using the near edge type thermal head in Figure 28; Figure 30 is a sectional view of an example of a conventional corner head type thermal head; Figure 31(a) is a sectional view of another example of the conventional corner head type thermal head; Figure 31(b) is a plan view of another example of the conventional corner head type thermal head; and Figure 32 is an illustration of a printing mechanism of a printer using the conventional corner head type thermal head. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the accompanying drawings, there are shown preferred embodiments of the invention. First embodiment: Figure 1 shows a sectional view of a first embodiment of the invention. Parts identical with or similar to those previously described with reference to Figures 32-34 are denoted by the same reference numerals in Figure 1. In Figure 1, a glaze layer 11 is formed near the end face on a substrate 10 and a resistance film layer 12 is formed on the glaze layer 11. The glaze layer 11 in the embodiment has the sectional form like a mountain. A discrete electrode 14 and a common electrode 15 are provided at a given interval to form a heater area 13 on the top of the mountain shaped portion, namely, the corner part 55. The resistance film layer 12, the discrete electrode 14, and the common electrode 15 are covered with a protective film 16. A slope 18 is formed from a heater area 13 to the side 17 of a substrate 10, as with the conventional thermal head examples. The resistance film layer 12 is formed on the slope 18 and the common electrode 15 is provided on the resistance film layer 12. In the slope 18, a reinforcement conductor 35 along the common electrode 15 is embedded below the resistance film layer 12. That is, the resistance film layer 12 is sandwiched between the common electrode 15 and the reinforcement conductor 35, and each of the common electrode 15 and the reinforcement conductor 35 is in electric contact with the resistance film layer 12. The invention is characterized by the fact that the reinforcement conductor 35 along the common electrode 15 is embedded in the slope 18 as described above, whereby power can be supplied to the heater area 13 by the common electrode 15 and the reinforcement conductor 35 in association with each other. Therefore, the overall electrical resistance of the common electrode 15 and the reinforcement conductor 35 is lowered, so that the voltage drop at the common electrode 15 can be decreased drastically. As described above, the effect of lowering the electrical resistance of the common electrode part can be accomplished by installing the reinforcement conductor 35 near the common electrode 15. Other embodiments of the invention for producing a similar effect to that of the embodiment shown in Figure 1 will be described. Second embodiment: A second embodiment of the invention shown in Figure 2 is an example in which a reinforcement conductor 35 embedded in a slope 18 reaches not only a substrate 10, but also a glaze layer 11, whereby the reinforcement conductor 35 can be formed in a wider area. Third embodiment: A third embodiment of the invention shown in Figure 3 is an example in which a reinforcement conductor 35 embedded in a slope 18 reaches the side 17 of a substrate 10. Fourth embodiment: A fourth embodiment of the invention shown in Figure 4 is almost the same as the third embodiment shown in Figure 1 except that the glaze layer 11 is of a full glaze type. Fifth embodiment: A fifth embodiment of the invention shown in Figure 5 is an example in which the sectional form of a reinforcement conductor 35 differs. Sixth embodiment: An sixth embodiment of the invention shown in Figure 6 differs slightly from the embodiment shown in Figure 1 in the sectional form of thermal head; a reinforcement conductor 35 in the sixth embodiment is similar to that shown in Figure 1. The embodiments shown above can be selected according to the application of the thermal heads. Seventh embodiment: A seventh embodiment of the invention is shown in Figure 7. The embodiment shown in Figure 7 is characterized by the fact that the corner head type thermal head with the entire slope 18 formed from the mountain top (corner part 55) in the heater area 13 to the side 17 of the end face of the substrate 10 as a convexly curved surface has the reinforcement conductor 35 along the common electrode 15 embedded below the resistance film layer 12 of the slope 18 as in the first embodiment. Eighth embodiment: An eighth embodiment of the invention is shown in Figure 8. The embodiment shown in Figure 8 is characterized by the fact that the corner head type thermal head with an intersecting part 20 of the slope 18 and the side 17 of the substrate 10 formed as a convexly curved surface has a reinforcement conductor 35 along a common electrode 15 embedded below a resistance film layer 12 of a slope 18 as in the first embodiment. As described in connection with Figures 7 and 8, the entire slope 18 or the intersecting part 20 of the slope 18 and the side 17 is formed as a convexly curved surface, so that if a ribbon is in sliding contact with the portion, the ribbon is not worn or cut. Next, a method of manufacturing a corner head type thermal head which is not an embodiment of the present invention is described. Figures 9 to 13 show the manufacturing steps of the thermal head. In the step shown in Figure 9, a mountain-like glaze layer 11 is formed on the top surface of a substrate 10. In the step shown in Figure 10, the glaze layer 11 and the substrate 10 are half cut with a blade 25 so as to leave a part of the glaze layer 11 from the top surface of the glaze layer 11 to the substrate 10. The blade 25 has a slant part 26 as a part of the side, the slant part 26 being formed as a concavely curved surface. To half cut them, the glaze layer 11 is cut with the slant part 26, thereby forming a groove 21 (Figure 11) having the inclined side constituted of the glaze layer 11 and the substrate 10. Thus, the glaze layer 11 side of the groove 21 formed by the half cutting is formed as a convexly curved surface. In the step shown in Figure 11, the substrate 10 where the groove 21 is formed by the half cutting is heat-treated. Burrs produced on the top 22 of the glaze layer 11 by the half cutting are removed by the heat treatment for rounding the top 22. The top 22 will become the corner part 55 shown in Figure 1 and 7. The glaze cut part on the face of the groove 21 formed by the half cutting is low in smoothness, but the smoothness of the face is also improved by the heat treatment. Thus, subsequent pattern formation is facilitated. Although not shown, the substrate 10 is a large substrate from which a large number of thermal heads can be provided, and a plurality of grooves 21 are formed. In the step shown in Figure 12, films of a resistance film layer 12, a discrete electrode 14, and a common electrode are formed by a photo-lithography process. In this case, the discrete electrode 14 and the common electrode 15 are spaced out to form a heater area 13 in the vicinity of the top of the glaze layer 11. Further, a protective film 16 is formed to provide the substrate before division as shown in Figure 12. Lastly, the substrate is cut and divided along the A-A line shown in Figure 12 to provide a separate thermal head shown in Figure 13. The corner head type thermal head is now complete. In the manufacturing method of the corner head type thermal head described above, grooves 21 are formed by half cutting and a predetermined pattern is formed, then separate thermal heads are produced by cutting or cracking, whereby a large number of thermal heads can be prepared easily and simultaneously. Figure 14 shows a printing mechanism of a printer using the corner head type thermal printer according to the invention. Print paper 30 and a ribbon 31 are put between the glaze layer 11 and a platen 51 and printing is performed by heat generation of the heater area 13. The slope 18 is formed at the end of the thermal head and the entire slope 18 or the intersecting part of the slope 18 and the side 17 of the substrate 10 is formed as a convexly curved surface, so that the ribbon 31 is in sliding contact with the smooth face and can be prevented from being worn or cut. Ninth embodiment: In the Above examples in which a substrate of partial glaze type is used are discussed, but the invention can also be applied to cases where a substrate of full glaze type is used. An example thereof is shown in Figure 15(a),(b). As shown in Figure 15 (a), a glaze layer 11 is formed fully on a substrate 10. The full glaze layer 11 is half cut with the above-mentioned blade 25, thereby forming a thermal head of the full glaze type with the end having a slope formed as a convexly curved surface, as shown in Figure 15 (b). Next, to manufacture the corner head type thermal head having an intersecting part 20 of the slope 18 and the side 17 formed as a convexly curved surface, a blade 25 of the form as shown in Figure 16 (a) may be used for half cutting. A slant part 26 of the blade 25 consists of a nose 27 formed as a concavely curved surface and a linear part 28. The rest of the steps are the same as the steps shown in Figures 11 to 13 and the thermal head shown in Figure 16 (b) is thus manufactured. Another method of forming the intersecting part 20 of a thermal head which is not an embodiment of the invention will be described in connection with Figure 17. The slant part of a blade to be used (not shown) may consist of a linear part, and a slope 18 is formed by the above-mentioned method, then the intersecting part 20 of the slope 18 and the side 17 of a substrate 10 is ground for chamfering. Next, a method of manufacturing the corner head type thermal head shown in Figure 1 will be described. Figures 18 to 23 show the manufacturing method of the thermal head. In the step shown in Figure 18, the glaze layer 11 is formed on the substrate 10. In the step shown in Figure 19, a dicing blade is used to form a groove 36 reaching the substrate 10 from the top surface of the glaze layer 11. In the step shown in Figure 20, conductor paste is embedded by printing or injection into the groove formed in the preceding step, and is calcined and hardened. The conductor paste 37 finally becomes the reinforcement conductor 35. In the step shown in Figure 21, a blade 38 with a slant part is used to half cut the glaze layer and the substrate so as to leave a part of the conductor paste 37 described in the preceding step for forming the slope 18 of the corner head type thermal head. If a blade with the entire slant part formed as a concavely curved surface as shown in Figure 10 is used as the blade 38, the slope 18 is formed entirely as a convexly curved surface, as shown in Figure 7 (seventh embodiment). If a blade with the nose 27 formed as a concavely curved surface as shown in Figure 16 (a) is used as the blade 38, the slope 18 is formed with the intersecting part 20 of the slope 18 and the side 17 of the substrate 10 formed as a convexly curved surface, as shown in Figure 8 (eighth embodiment). In the step shown in Figure 22, the substrate 10 where the groove 39 is formed by the half cutting is chemically treated or heat-treated for rounding the top 22 and improving the smoothness of the glaze cut part, as described above. A plurality of grooves 39 are formed as described in connection with Figures 9 to 13. In the step shown in Figure 23, the resistance film layer 12 and conductors to form electrodes 14 and 15 are formed by sputtering, etc., and the discrete electrode 14 and the common electrode 15 are patterned by photo-lithography. Next, the protective film is sputtered and last the substrate is divided to complete a separate corner head type thermal head shown in Figure 23. The manufacturing method is characterized by the fact that the conductor paste 37 is embedded in the groove 36 formed by the half cutting and that the slope 18 is formed so as to leave a part of the conductor paste 37 with the blade 38 with a slant part, whereby the structure where the reinforcement conductor 35 is embedded in the slope 18 is provided. Next, a method of manufacturing the fifth embodiment shown in Figure 5 which differs from other embodiments in the sectional form of the reinforcement conductor 35 will be described. Figures 24 to 27 show the manufacturing method of the corner head type thermal head. In the step shown in Figure 24, a blade 40 with a slant part is used to form a groove reaching the substrate 10 from the top surface of the glaze layer 11. The side wall of the groove containing the glaze layer 11 is a slope. In the step shown in Figure 25, conductor paste 37 is embedded in the groove as in the step shown in Figure 20. In the step shown in Figure 26, a blade 41 having a slant part whose slant angle is larger than that of the slant part of the blade 40 used in the step shown in Figure 24 is used to half cut the glaze layer and the substrate so as to leave a part of the conductor paste 37 described above for forming the slope 18 of the corner head type thermal head. In this case, the partially left conductor paste 37 becomes the reinforcement conductor 35. Subsequently, the steps as described in conjunction with Figures 21 to 23 are executed to complete the corner head type thermal head shown in Figure 27.

Claims: A corner head type thermal head comprising: a glaze layer (11) provided on a substrate (10); a slope (18) formed from a predetermined position on a top face of said glaze layer (11) to a substrate side (17); a convex corner part (55) formed by intersection of said slope (18) and the top face of said glaze layer (11); a resistance film layer (12) provided on said slope (18) and on said glaze layer (11); a heater area (13) formed lying across a top of said corner part (55); a common electrode (15) provided on said resistance film layer (12) in said slope area (18); and a discrete electrode (14) provided on said resistance film layer (12) in an area facing said common electrode (15) with said heater area (13) between; characterized, in that in the slope (18) a reinforcement conductor (35) associated with said common electrode (15) is embedded in the substrate (10) below the resistance film layer (12) so that said resistance film layer (12) is sandwiched between said reinforcement conductor (35) and said common electrode (15) in said slope area (18). The corner head type thermal head as claimed in claim 1, characterized, in that at least an intersecting part of said slope (18) and said substrate side (17) is formed as a convexly curved surface. The corner head type thermal head as claimed in 2, characterized, in that a full face of said slope (18) is formed as a convexly curved surface. A method of manufacturing a corner head type thermal head, comprising the steps of: forming a glaze layer (11) on a flat surface of a substrate (10); half cutting an area containing a part of said glaze layer (11) downward from a top surface of said glaze layer (11) for forming a groove (36); embedding a conductor (37) in said groove (36); preparing a cutting blade (38) having a slant part; half cutting said glaze layer (11) and said substrate (10) with said cutting blade (38) downward from a predetermined position on a top surface of said glaze layer (11) for forming a slope (18) with a part of said conductor (35) left from said glaze layer (11) to said substrate (10); heat-treating said substrate (10) and said glaze layer (11); forming a resistance film layer (12), a common electrode (15), a discrete electrode (14), and a protective film (16) on said glaze layer (11) and on said slope; and cutting said substrate (10) on both sides of a groove (39) having said slope as one side. The method as claimed in claim 4 wherein said slant part is formed as a concavely curved surface at least in a neighborhood of a nose of said cutting blade having the slant part. The method as claimed in claim 4 or 5 wherein a full face of said slant part of said cutting blade is formed as a concavely curved surface.

Inventors: OHNISHI HIROAKI, OHNISHI, HIROAKI, OHNISHI, HIROAKI, C/O ROHM CO.,LTD.
Applicants: ROHM CO LTD, ROHM CO., LTD.
Application year: 1994
Main classification: B41J2
IPC codes: B41J2